An increasingly common type of conveyor utilizes a substantially planar tray floor and a drive mechanism cyclically powered to move goods along the tray floor. Because only the conveyor tray contacts the material being conveyed, these types of conveyors are preferred in applications requiring high cleanliness, and are commonly used, for example, in the food processing industry. These conveyors thus have significant advantages over conveyors which utilize moving parts, such as belts or chains, which contact the conveyed products.
One type of conveyor which utilizes a cyclically powered tray is a vibratory conveyor, which employs a substantially planar tray floor with opposing tray sides. The stroke of a vibratory conveyor is relatively short, and typically is approximately 1/16th of an inch in length, so that the tray imparts an upward and forward motion to products supported on the tray. The tray is thus returned to its original position while the products are out of contact with the tray floor. While vibratory conveyors are widely used in the food processing industry, they have significant disadvantages which have been recognized for decades. The movement of products along the vibratory conveyor tray can be damaging to the products, and thus vibratory conveyors frequently are not desired when moving fragile products. Moreover, when moving products with a seasoning or coating, such as seasoned potato chips, vibratory conveyors are not favored since the vibratory motion tends to shake the seasoning or coating off of the products. In other applications, however, vibratory conveyors are widely accepted for moving products which do not have seasonings or coatings. Also, vibratory conveyor manufacturers have been able to reduce the amount of vibration imparted to the product while still maintaining an acceptable product flow rate along the tray. A exemplary vibratory conveyor is disclosed in U.S. Pat. No. 5,211,277.
Another type of cyclically powered trough-type conveyor is a linear motion conveyor. The stroke of a linear motion conveyor is much longer than for a vibratory conveyor, and typically is in the range of approximately an inch and a half The products move slowly forward with the linear motion of the conveyor tray, and the drive mechanism then returns the tray backward more quickly, thereby sliding the products along the tray. A linear motion conveyor has several significant advantages over vibratory conveyors, primarily because the tray motion is more gentle on the transported products. Linear motion conveyors are thus well suited for transporting fragile goods, such as snack foods. Since the products are not thrust upward off the tray supporting surface, seasoning loosely attached to the products remains on the products. Linear motion conveyors with an improved drive mechanism are disclosed in U.S. Pat. Nos. 5,351,807 and 5,794,757.
One of the drawbacks with early versions of linear motion conveyors was that the drive mechanisms could not rapidly start and stop the conveyor tray movement. These earlier versions of linear motion conveyors were nevertheless commonly used along main conveyor lines. Because of this slow start and slow stop limitation, however, linear motion conveyors were seldom used in cross feeder applications or as conveyors used to feed weighing scales. Newer designs of linear motion conveyors, as disclosed in the above referenced patents, have overcome this limitation, and the drive mechanisms disclosed in currently available linear motion conveyors are able to both start and stop the conveyor tray movement substantially instantaneously. Because of this ability, linear motion conveyors with these improved drive mechanisms are increasingly used in cross-feeder applications and in applications to feed weighing scales.
One of the problems with cyclically powered trough-type conveyors is that product irregularly fed to the conveyor tray tends to remain in that configuration as the linear motion conveyor moves the product along the conveyor tray. Because linear motion conveyors have gentle product handling characteristics, when piles of products are introduced to a linear motion conveyor, the piles thus tend to remain substantially as input to the linear motion conveyor and continue down the length of the tray without leveling out. Piles and voids of product along a linear motion conveyor tray provide irregular product feed rate to the downstream equipment, which then may adversely affect the performance of scales and other equipment which attempts to cope with this substantially irregular product feed rate. The irregular product feed rate from a linear motion conveyor is a significant problem, particularly when the conveyed product, like potato chips, tend to interlock together. Potato chips may thus be irregularly output from a seasoning tumbler to a linear motion conveyor, and irregularly shaped piles of potato chips move along the linear motion conveyor. Due to the shape of the conveyed product and the gentle motion of the linear motion conveyor, these product piles thus continue to travel down the conveyor tray, and are a significant problem to the reliable performance of weighing scales which are adversely affected by the substantially varying product output rate from the linear motion conveyor. Vibratory conveyors have some capability of reducing product piles along the tray due to the vibratory action on the product. As vibration is reduced, however, to accommodate products requiring more gentle handling, irregular product feed rate becomes more of a concern also for vibratory conveyors.
The disadvantages of the prior art are overcome by the present invention, and an improved cyclically powered trough type conveyor with a flow leveler is hereinafter disclosed for normalizing product flow along a linear motion conveyor tray.